The present invention generally relates to ink-jet printing, and in particular, to a cleaning solvent to assist in cleaning the printhead of an ink-jet printer.
Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on a print medium. The ink is ejected from a plurality of small nozzles located on the printhead.
During printing, stray ink, dust, and debris can accumulate on the printhead and obstruct or interfere with the proper ejection of ink. In addition, during periods of inactivity, ink can dry on the printhead thereby plugging or blocking the nozzles. Printhead servicing, including wiping the printhead with a cleaning solvent, minimizes the impact of these problems on print quality. To maintain print quality, the printhead must be routinely cleaned.
Ink-jet printers generally have printhead servicing systems to facilitate printhead cleaning. Typical printhead serving systems employing a wet-wiping method, such as those described in U.S. Pat. No. 5,914,734, usually function by wiping the printhead with a wiper that is associated with the cleaning solvent. Generally, the wiper serves to transfer the cleaning solvent to the printhead and wipe debris from the printhead. However, the cleaning solvent may also be transferred to the printhead independent of the wiper, as described in U.S. Pat. No. 5,907,335.
A cleaning solvent serves numerous functions. First, the cleaning solvent lubricates the wiper, providing better wiping function. Second, the cleaning solvent dissolves some of the dried ink accumulated on the printhead. Third, the cleaning solvent helps the wiper to transport debris off the printhead. Finally, as a thin layer of cleaning solvent is left on the printhead, the cleaning solvent also functions as a protective coating on the printhead making subsequently deposited stray ink or debris easier to wipe off.
Variations of some properties in a cleaning solvent, including viscosity, vapor pressure, solubility, hygroscopicity, and surface tension, affect the performance of the cleaning solvent. Various cleaning solvents, consisting of relatively viscous non-volatile liquids (such as polyethylene glycol (PEG)) or consisting of various compounds dissolved or dispersed in water, are known. For example, U.S. Pat. No. 5,905,514, issued to Rhoads et al., describes a PEG-based cleaning solvent using PEG of molecular weight between 200 and 400. U.S. Pat. No. 6,224,185, issued to Fassler et al., describes a cleaning solvent consisting of a dihydrosilane or trihydrosilane in water. U.S. Pat. No. 6,193,352, issued to Sharma et al., describes a cleaning solvent consisting of an aqueous solvent of a metal salt of a taurine surfactant. U.S. Pat. No. 5,917,512, issued to Weber et al., discloses a cleaning solvent primarily composed of water and ethylene glycol.
Known cleaning solvents demonstrate fluctuations in performance depending on the printer""s operating environment. For example, a solvent that performs well in a cold, dry environment may be inefficient in a hot, humid environment. In addition, incompatibility between the ingredients of the cleaning solvent and the ingredients of the structure of the printhead and ink-jet ink are frequently known to occur. These incompatibilities lead to clumping and blockage of the printhead nozzles and thereby degrade the printhead.
In view of the shortcomings in the art, there remains a need for a cleaning solvent that will not degrade the printhead, does not interact with the ink ingredients, and exhibits exceptional performance regardless of environmental conditions.
In accordance with the present invention, cleaning solvents suitable for use in ink-jet printhead servicing systems and methods for formulating the same are provided. A specific cleaning solvent comprising glycerin and a polyhydric alcohol, such as 1,3-propanediol, is disclosed.
Glycerin has high water retention, a desired characteristic of a printhead cleaning solvent, but is quite viscous. Since the viscosity of glycerin is tempered by absorption of ambient water from the air, glycerin functions adequately as a cleaning solvent in humid conditions. However, in dryer environments, glycerin becomes viscous, which requires applying a larger amount of glycerin to the printhead for adequate cleaning. In addition, minor changes in temperature can significantly affect the viscosity of glycerol. However, the addition of a structurally similar compound, such as 1,3-propanediol, has been found to decrease viscosity while leaving intact the other desirable printhead cleaning characteristics of glycerin. The cleaning solvent formulations of the present invention provide optimal viscosity, vapor pressure, solubility, hygroscopicity, and surface tension to ensure acceptable cleaning of the printhead regardless of the operating environment.